Your home page is not loading, but can you login?
IF you can login to WordPress, what are your permalink settings? (Settings>Permalinks)
try clicking the "save" button on permalinks twice.
on the bottom of the permalinks setting page, does it give any messages about your .htaccess file?

Also, from a command prompt, run: sudo chown -R www-data:www-data /var/www
this will give permissions to apache for any files that might have other permissions.

after each of those steps, clear your browser cache and reload your home-page by holding down shift while reloading.

If none of those things work, then you might start dinkering with Apache (check error logs from command-prompt like so: sudo tail -f /var/log/apache2/error.log